Contamination detection compositions



July 7, 1964 v. DvoRKovlTz Eil-AL 3,140,262

coNTAmNATroN DETECTION couposr'rlous Original Filed Dec.5, 1955 2 Sheets-Sheet. 1

5y MAMM: Sm@

July 7, 1954 v. DvoRKovlTz ETAL 13,140,262

`CONTAMIMTI0N `DE'IECTLfON- COMPOSITIONS Original Filed Dec. 5, 1955 2 Sheets--Snee'fl 2 United States Patent O M CNTAMDATIN DETECTIQN CNWSTNS Vladimir Dvorkovitz, Kansas City, Mo., and Neil Berst,

Evanston, and Susan Krause, Skokie, Ill., assignors to The Diversey Corporation, a corporation oifHIilinois Olflgillal application Dec. 5, i955, Ser. No.` 551,021, now

Patent No. 2,968,733, dated Jan. 17, 19,61, Divided and this application June 3, ,1959, Ser. No. 817,900

6 Claims. (Cl. 252-301.1)

This invention relates to radioactive materials, particularly to tracer compositions which are useful in determining the presence and location f contamination. More speciiically, this invention relates to tracer solutions containing radioactive isotopes which emit detectable gamma radiation and are capable of being selectively retained by contamination which induces or sustains bacterial activity in processing or conduit systems and the like, thereby permitting the detection of the presence and location of said contamination.

The terms tracer solution and tracer solutions are intended to include 'tracer materials or radioactive isotopes. For example, the terms include solutions or materials tagged with a detectable gamma ray-emitting isotope plus other constituents.

In the food processing industry it is often necessary to determine whether there is any contamination in the processing or conduit systems and the like after the systems have been rinsed or Washed with cleaning materials such as water and detergent solutions. The conventional bacteriological methods employed in detecting contamination (i.e., food contamination) in procesing or conduit systems require at least about 48 hours. Our method contemplates the utilization of materials containing radioactive isotopes that emit detectable gamma radiation and at the same time are capable of being used to selectively locate the presence of contamination in a period as short as about 1/2 hour.

The present invention is particularly useful in cases wherein the equipment under surveyance cannot be visually examined as Well as cases wherein sections cannot bereadily separated from the system and examined.

Once the particular equipment or section containing contamination is located, said equipment may be removed from the processing or conduit system and decontaminated by treating or scrubbing same until gamma radiation emanatingtherefrom does not exceed, or materially exceed, background radiation. If desired, the equipment or section may be decontaminated; that is, the contaminated material plus the tracer material or solution retained by said contamination may be removed by passing cleaning material through the system until said equipment or section does not emit a substantial amount 0f gamma radiation.

In order to selectively locate contamination, it is essential that contamination-free surfaces of the processing or conduit system and the like do not retain substantial quantities of the tracer material or solution. Therefore our method requires that a sufficient portion of the internal surfaces of the equipment employed in the processing or conduit system should be suiiiciently hard, smooth, nonporous, cleanable and free from cracks, leaks or other similar interfering 4deformations so as to permit the selective detection of contamination with tracer materials or solutions. If a pump is used to circulate the tracer material through the system, the internal surface of the pump should likewise be constructed of material possessing these properties. lf necessary, the tracer material or solution may also be effectively removed from defective and/ or contamination-free conduits or processing `equipment by the use of cleaning materials (i.e.,

3,140,262 Patented July 7, 1964 ICC of being detected by detection devices such as a'scintillation counter plus a sealer recording unit or a survey recording meter. i A

One of the critical features of our contaminationdetection method and the tracer materials employed therein is that undesired gamma ray-emitting isotope material may be selectively removed from the system (i.e., by rinsing the system with Water) without materially removing radioactive tracer material that is retained by contamination, thus enabling the detection devices to more readily locate contamination.

The particular radioactive tracer material employed in this method of selectively locating contamination should be capable of being selectively removed from the equipment or conduits and should not 4materially adhere to the surfaces of clean (i.e., contamination-free) equipment or conduits. The tracer material should preferably have a suicient half-life so as to be capable of reuse and of maintaining relatively consistent,detectable activity for at least one day or more. In addition, tracer materials should preferably possess a suiiiciently short half-life so as to avoid undue hazards that may result from accidental spillage and be capable oi an expeditious rate of decay after being used lfor contamination-detection purposes.

The particular radiation energy (i.e., mev.) of the tracer material selected for use in our method of selectively locating contamination rnust be sufficiently great so as to penetrate through the thickness of the equipment or system being inspected and should aiiord safe and convenient handling and yet be capable of providing a detectable radiation count above background without requiring excessive shielding. The avoidance of materials that emit radiation of excessively high energy reduces exposure hazards as Well as the reflection of radiation energy off surrounding surfaces. It is desirable to be able to detect contaminationtrom a reasonably close distance from the equipment (i.e., about 1 to 5 feet or less). In addition, the radiation energy should be suiiiciently 10W so as to obviate the need for employing excessive precautions in handling or storing the gamma rayemitting tracer material.

The concentration of radioactivity (i.e., millicuries or microcuries per unit volume of solution) of the tracer solution containing the radioactive isotope must be high enough to b e eiectively retained by contamination. The particular concentration of radioactivity :selected will depend upon the composition and thickness of the processing equipment or conduit system and the amount of radioactive energy of the isotopethat isemployed in the tracer solution. The amount of radioactivity that is retained by the contamination may be increased `by increasing the radioactivity concentration of the tracer solution. By increasing the rate of flow of the tracer solution through the system and length of time which it is permitted Vto Contact contamination, the contamination `will` have a greater opportunity for retaining the tracer material or solution.

Gamma ray-emitting radioactive isotopes such as 1131 may be incorporated into the tracer solution and used in our contamination-detection method. For example, compounds such as diiodouorescein tagged with 1131 have been found to produce satisfactory results in contamination-detection. If desired, tracer solutions containing Br82 and K42 and the like may be used. It is desirable that the particular material with which the radioactive isotope is combined or used be capable of being dissolved in a liquid carrier or vehicle; for economic reasons, the material containing the isotope should be soluble in an aqueous solution.

Radioactive isotopes such as Na22 may be contained in the tracer solution if an isotope having a long half-life is desired, such as for experimental purposes.

Improved results may be obtained if the tracer solution contains (a) a salting-out agent that induces the adsorption and/ or absorption of the radioactive isotope-containing compound or material onto contamination and/or (b) anionic and/ or nonionic low-foaming wetting agents that tend to minimize the retention of the tracer material or solution on contamination-free surfaces of the equipment, conduits or other elements of the system.

Salting-out agents, such as sodium carbonate, sodium sulfate, sodium tripolyphosphate, and the like, satisfactorily induce the precipitation of the tracer material or solution onto contamination.

Wetting agents such as Triton X-100 (isooctylphenyl ether of decaethylene glycol) produced by Rohm and Haas Co., Hyonic P.E.-225 (a polyoxyethylene condensate of mixed fatty and rosin acids), produced by Nopco Chemical Co., and the like may be used to minimize the etention of the tracer material or solution on clean suraces.

In addition, mixtures of salting-out agents and wetting agents may be used, such as Oronite D-40, produced by Oronite Chemical Co. (about 40% by weight sodium dodecylbenzene-sulfonate and about 60% by weight sodium sulfate) as well as a mixture of a catalyst such as sodium sulfate plus a polyoxypropylene-polyoxyethylene-type nonionlc surface-active agent such as Pluronic-type materials (i.e., as illustrated in U.S. Patent No. 2,674,619) marketed by Wyandotte Chemicals Corporation and as exemplilied by Pluronic L-62 [HO (C2H4O) a (Cal-ISO) b (C2H4O) CH having a molecular weight of about 2000], and the like.

In addition to the above materials, the tracer solution may contain, if desired, an vantifoam component such as D.C. Antifoam A (dimethyl siloxane) produced by Dow Corning Corporation. However, in selecting an antifoam component, care should be exercised in order to avoid materials that will result in their being precipitated out of solution onto the equipment being examined.

Since the radioactivity of the tracer material will dimlnish with time, its radioactivity may be replenished by the addition of more radioactive tracer material (so as to maintain a desired or effective radiation concentratlon), and the solution may be recycled or recirculated through the system.

The volume of the radioactive tracer solution should be sufficiently great so as to provide effective contact of said tracer solution with the surfaces of the system being examined. The Volume of the tracer solution may in many cases be reduced by spraying readily accessible internal surfaces of the equipment under examination.

In the accompanying drawings:

FIGURE 1 is a diagrammatic perspective view of the system employed in the tests set forth in hereinafter described Example l; and

FIGURE 2 is a diagrammatic perspective view of the system employed in the tests set forth in hereinafter described Example '3.

In a preliminary experiment a small pilot plant was set up consisting of a pump, a -gallon kettle, and a stainless steel pipe 4 feet long. Cooked pea slurry was circulated through this closed system for one day. External heat was applied locally over a small area on the pipe in TABLE I Counts per Counts per No. Location Minute Minute Counter Before After Cleaning Cleaning 1 a, 712 640 2 2, 240 576 3 3, 584 704 4 4, 544 576 5 3, 200 512 Background 400 400 It was observed that all the counts which were substantially above background after contamination were in close proximity to the heated area, the point having the highest count, i.e., 4, being the exact point where heat was applied.

It will also be noted that after cleaning the counts were reduced to practically background. These tests, therefore, show a definite retention of radioactivity by the contaminated surface and reduction of activity to background on the surfaces after cleaning.

Referring to FIGURE 1, the steel kettle 1 (stainless steel 316-4) has about a 30 gallon capacity, a wall thickness of about 1A inch and is adapted to be iitted with a mixer and heated with steam. The pipes are stainless steel B16-2B pipes having an outside diameter of about 1.5 inches and a wall thickness of about 0.05 inch. The ilow through the system starts from tank 1, continues through pipe 2 to the large Waukesha pump 17, continues through pipes 3, 4, 5 and 6 to the small Waukesha pump 18 and returns to the tank through pipes 7, 8, 9, 10, 11, 12, 13 and 14. A valve 19 is placed in the return line 13 just before it enters the top of the tank in order to permit emptying of the system. If desired, the tracer solution may be reused for subsequent runs by adjusting the valve 19 and removing the tracer solution from the system through pipes 15 and 16. About 1 gallon of liquid is retained in the pipes after the system is drained through the outlet 16. This system was used in the test set forth in Example 1.

EXAMPLE 1 In order to assure the retention of contamination within the system, sections of pipe were removed from the system, coated with the cooked product being tested, and heated in an oven until contamination was thoroughly baked onto the pipes. The pipes were then placed in their respective positions in the system and various tests were started. This procedure permits an evaluation of sections of contaminated and clean pipe with reasonable control over both conditions.

Water was then run through the system to check for leaks and to remove any loose contamination. Thus, only the tenacious baked-on contamination remained for the final test with NaI131 solution. The system was then drained and about 5 gallons of fresh water was added to the tank. The total volume within the system was thus about 6 gallons. Various concentrations of NaI131 were circulated through the system on the basis of a volume of about 6 gallons of solution. The NaI131 was added to the tank and circulated in the system. After the tracer solution was removed from the system, the system was rinsed three times with clear Water and surveyed for radioactivity with a scintillation counter. At this. point all unshielded radioactive sources were completely removed 'from the vicinity of the system.

The following detergent was used for decontaminating clean and food-contaminated stainless steel pipes:

Percent by weight Sodium carbonate 59L77 Sodium tripolyphosphate 22 Sodium metasilicate pentahydrate 16 Sodium dodecylbenzenesulfonatei 1 Octylphenylpolyoxyethylene ether 1 Carboxymethylcellulose 0.23

The following tests in Example 1 were run using a baked-on contamination applied as previously described. Sections of pipe were removed from the system and coated with cooked food which was baked-on in orderto assure thegknown locations of contamination.

In Test No. 1 pipes 6 and 8 were removed from the system, coated with fruit dessert which was baked-on and placed back into their respective positions in the system. About gallons of water was circulated through the system for about 2 minutes to c heck for leaks. The system was then drained andan additional 5 gallons of water was added to the system to give a total volume of about 6 gallons ofwater within the system (an allowance of about l gallon is made for hold-up in the pipes following draining). About 8.4 millicuries of Nall31 was placed into the tank 1. The resulting solution was circulated for about l5 minutes and the system was subsequently drained and rinsed with three 10 gallon portions of water. Various points in the system were checked by holding the scintillation counter at a distance of about Aone foot. theresults of this test are shown in Table II.

The background reading of `Testtlio. 1 was obtained after the `equipment was `contacted with thertracer solution, drained, `and rinsed. This reading is somewhat higher than the background level obtained before such a, test is made due tothe contribution to the overall activity from the pump 1,8 and the contaminated pipes. When all of the equipment was de ontaminated and no isotopes were present in the room, the background was Z50-260 counts per minute, which is normal background obtained with the scintillation counter.

As indicated in Table II, contaminated pipes 6 and 8 gave (high) counts that were easily determinable over the background level.

It was found that some loose contamination lodged in the small pump 1,8 was one factor contributing to the rather high activity at this point. Upon the disassembly and examination of pump 18, it was found that the rough and porous condition of the face plate caused it to retain a rather high radioactive count. Since pipes 6 and 8 were contaminated in the same manner, the recorded count of pipe 8 when read on the side adjacent to the pump 18 was probably partially influenced by reiiection from the small pump 18. This conclusion was veriiied by, notingthe count of the same `pipe on theside opposite the` pump, thehresult was `only 1,216 oiints per minute.

`,Whenfthe pump y13 vwas partially shielded with lead bricks the pipe `5i ,gave only .2,942 counts `per minute` on the side adjacent the pump 18 compared to 4,930 counts per minute without shielding. This appears to further indicate the importance of eliminating stray activity from the area being surveyed.

A number of points in Test No. l that were known to be clean such as pipes 9 and 4 as well as the large pump 17 gave counts virtually equal to background.

Test No. 2 was a survey of the same points shown in Table II; however, the scintillation counter was used at a distance of only about two inches from the equipment instead of one foot. The results from this survey are shown in Table III.

TABLE III No. Location Counted Counts per Frorn 2) Minute 448 3, 840 960 15, 744 3, 060 360 D 320 Large Pump 17 400 `Background.; 320

The data tabulated in Table III appears to` indicate that the scintillation counter serves as ta shield when used close tothe surface being surveyed. For example, the pipe 8 does not have the high count from reflection that is shown in Table II. In general, it may be concluded that the differences between contaminated and uncontaminated areas are more sharply dened by holding the scintillation counter close Vto the area being surveyed. Such a method appears to have .the additional advantage of providing some shielding from stray activity by the bulk of the scintillation counter itself.

Before starting the remaining series of tests in Example I, the small pump 18 was decontaminated with a boiling solution of 4 ounces per gallon of a 95% by weight caustic and 5% by weight `sodium tripolyphosphate mixture.

Test No. 3 was run using (a) fruit dessert, (b) vegetable, liver and bacon soup, and (c) sweet potatoes baked onto separate sections of the system (e.g., pipe 6 was contaminated with fruit dessert; pipe 11 was contamined with sweet potatoes; pipe 8 and elbow 21 were contaminated with soup). Water was run through the system to check for leaks. About 6 gallons o f tracer solution containing about 5.0 millicuries of NaI131 was circulated in the system for about 30 minutes. The system was drained, rinsed and surveyed. The data obtained from this test is shown in Table IV. The scintillation counter was held 2 inches from the area being surveyed.

TABLE IV No. Location Counted Counts per (From 2 in,) Minute Pipe 11 (contaminated 832 with sweet potatoes) Pipe 9..---; 384

Pipe 8 (contaminated 704 with soup) Elbow 21 (contami- 896 nated with soup) Pipe 6 (contaminated 896 with fruit dessert) Small Pump 18... 5, 696

Pipe 4.. 384

Large Pump 412 Background. Y 256 The data shown in Table IV eiiectively illustrates that contamination may be detected and located by use of tracer solutions and our contamination-detection method. Each `of the contaminated pipes gave activity counts `of 700-900 counts per minute while the uncontaminated pipes 4showed 384 counts.

The small pump 18 ,again gave a rather high count,

and it was found that a considerable amount of loose contamination had settled in the pump. Care was taken upon the weight of the iinal solution which contains the additive, Water, and NaI131.

Test No. 1

TABLE V Counts per Minute Coneen- Conoen- Type and tration of tration of Finish of With Additive Without Additive Sample Name of Additive, Activity, Type of Food Con- Stainless No. Additive Percent Microcuries tarnnation per Liter Contami- Clean Containi- Clean nation Side uated Side Side Side 8 240 Vegetable, Liver B21-21)---- 491.0 16.8 366. 7 485. 4

and Bacon.

8 220 Chocolate Custard. B16-2B 886. 6 14. 2 281. 1 92. 5

10 220 Prunes 304-2B 2, 108. 7 130. 0 1, 431. 2 64. 5

to count all other portions of the system from such a position that reflection from the pump 18 was minimized. It was found that the metal in the housing of the small pump retained a rather high level of activity after being subjected to a normal cleaning procedure. This indicates the desirability of employing equipment having nonporous, smooth, hard surfaces in the system. The large pump 17 retained practically no activity, thus indicating that pumps may be used in the system Without jeopardizing contamination-detection.

EXAMPLE 2 Duplicate l inch square coupons of various stainless steels were precleaned for 5 minutes in a cleaning solution (e.g., boiling aqueous solution containing 4 ounces per gallon of a 95% caustic and 5% sodium tripolyphosphate solution), rinsed with water, dried, contaminated on one side with food, andagain dried. One of each duplicate coupon was suspended for 2 minutes in a stirred solution of Nal131 containing an additive (i.e., salting-out agent and/or wetting agent) While the remaining coupon was suspended in a Nal131 solution that did not contain an additive. The concentration of each of the Nal131 solutions was about 200 microcuries per liter. The coupons were then rinsed by dipping them in three successive beakers of water; following rinsing, the coupons were counted on both sides with a halogen tube counter. Since a halogen tube counter is generally sensitive only to beta radiation, it is possible to get accurate counts of both the contaminated and uncontaminated sides of the coupons with this instrument; beta radiation is shielded by the steel coupon so that the counter only registers the activity which it directly sees, e.g., the surface that faces the counter.

This procedure was followed in Test No. 1; however, minor modifications, as hereinafter described, were made in performing some of the other tests set forth in this example.

Test No. l was run using (a) vegetable, liver and bacon soup., (b) chocolate custard, and (c) prunes as the source of contamination. Table V indicates the beneficial results that are obtained with the use of the materials therein indicated. The concentration of the additive is based In Test Nos. 2-5, 3A inch diameter circular discs of type 304-2B stainless steel were used, and prunes that 5 were dried onto the discs by the application of heat were used for contamination. However, each of said tests required the use of different solutions.

Test No. 2 involved the use of NaI131 at a concentration of 100 microcuries per liter of solution. Table VI shows the readings that were obtained in Solution No. 1 which had a NaI131 concentration of 100 microcuries per liter of solution plus 5% by Weight (based upon the total weight of the Water, Nall-31, plus sodium tripolyphosphate) sodium tripolyphosphate, and Solution No. 2

Which contained NaI131 at a concentration of 100 microeuries per liter of solution. The data set forth in Table VI indicates that sodium tripolyphosphate appreciably increases the amount of activity retained by contamination and tends to reduce the amount of activity retained on clean surfaces.

Test No. 2

TABLE VI Counts per Minute Solution No. 1 100 mc./ Solution No. 2-100 mc./

liter N aI131+5% STPP liter NaI13I Contami- Clean Contami- Clean nated Side Side nated Side Side l, 324. 8 86. 4 935. 6 264. l l, 024. 8 94. 7 893. 3 264. 2 1, 004. 5 87. 7 906. 7 169. 6 1,019. 8 46. 3 978. 8 434.8 1, 207. 8 92. 7 902. 5 108. 4 l, 080. 8 134. 7 78.8. 5 257.0 1, 236. 8 129. 8 925. 4 270. 7 1, 107. 8 143. 5 770. 1 160. 6 1,307.8 59.6 668.8 68.6 l, 269. 8 96. l 664. 2 100. 4 1,326.8 141.2 861.1 110.7

In Test No. 3, the test solutions had a NaI131 concentration of 124 microcuries per liter of solution. Table VII indicates the readings that Were obtained with Solution No. l which had a Nal131 concentration of 124 microcuries per liter of solution plus 2% by weight (based small pump 18. The flow from the small pump 18 to outlet 16 and the tank 1 is similar to FIGURE 1.

Pipe 28 is type 316-2B stainless steel pipe having an outside diameter of about 1.5 inches and a Wall thickness of about 0.05 inch. Elbows 23 and 25 have drain outlets 30 and 31, which are controlled by valves 24 and 26 respectively. l

, Section 22 is constructed of several diary pipes that are coupled by a variety of fittings that are representative of the types commonly employed by the dairy industry. Pipe 21 is a Pyrex glass pipe having an inside diameter of about 1.5 inches Aanda wall -thickness of about /32 inch; the remaining pipes of section 22 are of type 304-4 stainless steel pipes having an inside diameter of about 1.403 inchesand a wall thickness of about 0.051

inch.

EXAMPLE 3 The following testy indicates that when material such as Oronite D-40 is incorporated with radioactive material such as Nalm, lower concentrations of Nal131 may be used in order to determine the presence of contamination as well vas its location:

One pipe that is located between section 22 and the small pump 18 is contaminated with a baked-on fruit dessert, while a second pipe which is located between the pump 18 and the tank 1 is contaminated with baked-on sweet potatoes.

A radioactive solution containing about 1.7 millicuries of Nal131 per 6 gallons (about 0.28 millicury per gallon) of solution .containing 1/z% of Oronite D-40 is then circulated within the system for 5 minutes. In order to prevent excessive foaming, a small amount of D.C. Antifoam A may be added to the solution.

Readings may then be taken of section 22, the contaminated pipes and the joints located at the extremities ofy said contaminated pipes with a scintillation counter and survey recording meter. The results of these readings Will indicate that the location of food contamination may be determined with a tracer solution of a relatively low radioactivel concentration when materials such as Oronite D-40 are incorporated in the tracer solution.

When the same contaminated pipes and procedure are used with tracer solution containing a NaI131 concentration of about 1.7 millicuries per 6 gallons of solution containing 1/2% of Oronite D-40, substantially similar readings will be obtained as those recorded when the concentration of NaI131 is 3.4 millicuries per 6 gallons of solution.

The contamination-detecting solution of the invention should preferably contain at least about 124 microcuries per liter of radioactive isotope and at least about 1.2% by weight of the salting-out compound or compounds (e.g., alkali carbonate, alkali sulfate and/or alkali tripolyphosphate). Similarly, the water-soluble composition used to preparethe working solution should have sullicient salting-out agent so that the solution contains at least about 1.2% by weight of the salting-out agent when the .concentration of radioactive isotope is about 124 microeuries per liter.

This application is a division of our copending application Serial No. 551,021, filed Dec. 5, 1955, now U.S, Patent No. 2,968,733, granted Jan. 17, 1961, which in turn is a continuation-in-part of our copending application Serial No. 542,173, filed Oct. 24, 1955, now aban- 5 doned. The method of detecting contamination herein disclosed is claimed in said application Serial No. 551,021.

The term system s shall hereinafter refer toAequipment (i.e., processing equipment, conduits, pumps, etc.) in which the presence of contamination as well as its location may be determined by utilizing tracer solutions containing detectable gamma radiation in the manner herein described.

The phrase promotes bacterial activity, when used with reference to contamination, shall hereinafter refer to contaminationY that induces or sustains bacterial activity.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such variations and modifications are considered to be within the purview and scope of the invention and the appended claims.

We claim:

1. A water-soluble tracer composition suitable for preparing an aqueous solution for determining the presence and location of contamination which promotes bacterial activity consisting essentially of a gamma rayemitting radioactive isotope selected from the group consisting of Na22, 1131, K42, and Br82 and a compound selected'from the group consisting of alkali carbonates, alkali sulfates, alkali tripolyphosphates, and mixtures thereof, said compound being present in said composition in an amount sufficient to produce a solution containing at least about 1.2%, by weight, based on the total solution, of said compound, when said composition is dissolved in water to produce a solution containing at least 124 microcuries per liter.

2. The composition of claim 1 which contains in addition a synthetic organic wetting agent selected from the group consisting of nonionic and anionic wetting agents.

3. A water-soluble tracer composition suitable for preparing an aqueous solution for determining the presence and location of contamination which promotes bacterial activity consisting essentially of a gamma ray-emitting radioactive isotope selected from the group consisting of Na, 1131, K42,` and Br82, sodium dodecylbenzene sulfonate, and sodium sulfate, said sodium sulfate being present in said composition in an amount sufficient to produce a solution containing at least 1.2%, by weight based on the total solution, of said sodium sulfate when said composition is dissolved in water to produce a solution containing at least 124 microcuries per liter.

4. A tracer solution suitable for determining the presence and location of contamination which promotes bacterial activity consisting essentially of water and a sufficient quantity of the composition of claim 1 to produce a solution having at least 124 microcuries per liter of solution.

5. The tracer solution of claim 5 which contains in addition a synthetic organic wetting agent selected from the group consisting of nonionic and anionic wetting agents. s

6. The tnacer solution of claim 5 which contains sodium dodecylbenzene sulfonate and sodium sulfate.

References Cited in the file of this patent UNITED STATES PATENTS 2,522,447 Harris Sept. 12, 1950 2,637,536 De Ment May 5, 1953 2,835,699 l Fries May 20, 1958 2,878,392 Polito Mar. 17, 1959 FOREIGN PATENTS 763,547 Great Britain Dec. 12, 1956 OTHER REFERENCES Bradford: Radioisotopes in Industry, pub. 1953 by Reinhold Pub. Corp., of N.Y., pp. 101, 291, 292.

Nucleonics, July 1955, page 23.

Geyer et al.: Peaceful Uses of Atomic Energy, vol. 9, pp. 19-23, Aug. 20, 1955. 

1. A WATER-SOLUBLE TRACER COMPOSITION SUITABLE FOR PREPARING AN AQUEOUS SOLUTION FOR DETERMINING THE PRESENCE AND LOCATION OF CONTAMINATION WHICH PROMOTES BACTERIAL ACTIVITY CONSISTING ESSENTIALLY OF A GAMMA RAYEMITTING RADIOACTIVE ISOTOPE SELECTED FROM THE GROUP CONSISTING OF NA22, I131, K42, AND BR82 AND A COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALKALI CARBONATES, ALKALI SULFATES, ALKALI TRIPOLYPHOSPHATES, AND MIXTURES THEREOF, SAID COMPOUND BEING PRESENT IN SAID COMPOSITION IN AN AMOUNT SUFFICIENT TO PRODUCE A SOLUTION CONTAINING AT LEAST ABOUT 1.2%, BY WEIGHT, BASED ON THE TOTAL SOLUTION, OF SAID COMPOUND, WHEN SAID COMPOSITION IS DISSOLVED IN WATER TO PRODUCE A SOLUTION CONTAINING AT LEAST 124 MICROCURIES PER LITER. 